A heat pipe is a mechanism that can transport a large amount of heat by evaporating and condensing a working fluid sealed in an airtight container even in the case of small temperature difference. This working fluid is sealed in liquid state after evacuating the airtight container. Thus, inside the airtight container, the vapor and the liquid are present in a mixed state, the vapor being equilibrium with the saturated vapor pressure of the working fluid.
When one end of the heat pipe is heated and the other end is cooled, the vapor evaporated from the liquid in the heating section quickly flows toward the cooling section. Thereafter, the vapor having reached the cooling section condenses and returns to the liquid state, and then is refluxed toward the heating section. By the circulation of the working fluid accompanied by such a phase change, the heat quantity is transported from the heating section to the cooling section.
A wick type heat pipe, a closed two-phase thermosiphon, and a loop type heat pipe are known as representative examples of conventional heat pipes. In the wick type heat pipe, a capillary pressure is generated by a wick in which a capillary structure such as fine grooves and porous material including, e.g., a wire mesh, fiber, and sintered metal is formed, and the liquid condensed in the cooling section is refluxed to the heating section.
The closed two-phase thermosyphon condenses the vapor, which is generated in the heating section at the lower end of the container, at the cooling section at the upper end of the container so as to return the vapor into the liquid state, and refluxes this liquid to the heating section by gravity or centrifugal force. The loop type heat pipe separates the respective flow paths of the vapor and the liquid that are bidirectionally moved between the heating section and the cooling section.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 1992-366391
The closed two-phase thermosyphon is superior to the wick type heat pipe in at least the following three points. Firstly, the thermal resistance of the heating section and the cooling section is small due to the absence of the wick. Secondly, since the capillary pressure is not used to reflux the liquid, there is no limit to the maximum heat transport amount due to the capillary limit pressure. Thirdly, there is no limit to the maximum heat transport amount due to dryout in which a liquid film does not reach the heating section, dry surface appears, and the heat transfer coefficient abruptly decreases.
However, in the closed two-phase thermosyphon, the flow of vapor and the flow of liquid are opposed to each other and this causes the following problem. That is, when the flow velocity of vapor increases in the closed two-phase thermosyphon, the liquid being refluxed is blown back by the flow of the vapor and thus increase in heat transport amount is restricted. Although the above-described problem in the closed two-phase thermosyphon is solved in the case of the loop type heat pipe, the loop type heat pipe has various problems caused by complexity of routing flow piping in which the flow of vapor and the reflux of liquid are separated from each other.
In view of the above-described problems, an object of embodiments of the present invention is to provide a heat pipe that simplifies configuration of a flow path while separating the flow of the working fluid in gaseous state from the reflux of the working fluid in liquid state.